In-pipe vehicles which require centering within the pipe are normally supported by polymer cups, wire brushes, or several wheels on independently spring loaded lever arms. The former two generate high levels of frictional resistance, and the latter requires relatively stiff springs on the lever arms partially to counteract the load exerted by the opposite lever arms. Therefore centralising a vehicle in a pipe to within accurate limits, while maintaining some automatic adjustment for variations in pipe size, is difficult to achieve and requires large forces, thus high frictional resistance to linear motion of the vehicle, and high resistance to traversing a pipe of reducing diameter.